In wireless communication networks based on the Long Term Evolution (LTE) standards, it is known for a wireless communication device to operate with a downlink bandwidth that matches the downlink bandwidth used by the supporting network base station, at least with respect to a given downlink carrier. In this context, the Third Generation Partnership Project (3GPP) refers to wireless communication devices as “User Equipments” or “UEs” and refers to base stations as “eNodeBs” or “eNBs.”
In LTE, a “resource block” or “RB” is the smallest unit of radio resources that can be allocated to a user and it “contains” a defined number of Orthogonal Frequency Division Multiplex (OFDM) subcarriers over a defined interval. Thus, the overall bandwidth used on the DL may be expressed in terms of the number of resource blocks spanned by that bandwidth. Any particular set or sets of subcarriers within a given interval may be identified by identifying the corresponding RB number or numbers. That is, the network may number the DL RBs starting with a lowest number for the lowest frequency, or vice versa, and sequentially number the RBs going up or down from that starting point. Of course, other numbering schemes may be used.
In a non-limiting example, bandwidth is measured in the number of RBs, where each RB corresponds to a fixed number of OFDM subcarriers. The number could be one, two, twelve, twenty-six or any other number. Without loss of generality, one may assume that a base station in the wireless communication network counts or references its downlink radio resources in terms of RBs. e.g., starting with a low RB number for a low frequency and a higher RB number for a higher frequency. Of course, the opposite order may be used. In either case, a base station numbers the RBs comprising its overall downlink bandwidth using a numbering scheme, where each number identifies or points to a particular RB within the downlink bandwidth.
In LTE. User Equipments (UEs) are configured to process the downlink bandwidth used by their supporting eNBs, at least on a per-carrier basis. Because the UE operates with the same bandwidth as the eNB, at least with respect to individual carriers, the UE had the same “view” of the radio resources and the same resource numbering scheme could be used in common between the eNB and the UE. Consequently, a resource pointer transmitted by the eNB using its numbering scheme can be received and interpreted by the UE without ambiguity.
However, it is appreciated herein that resource identification becomes decidedly more challenging to manage in new radio systems, also referred to as “5G” radio systems, which are being developed and deployed. In such radio systems, a given UE may support or be allocated only a subset of the overall downlink bandwidth associated with a network base station, and the location or position of the allocation within the overall downlink bandwidth may vary. By way of example, see TS 38.801, Study on New Radio Access Technology.
As a further complication appreciated herein, in LTE, Physical Downlink Control Channels (PDCCHs) are potentially transmitted over the entire (downlink) bandwidth, which requires individual UEs to monitor for PDCCH over the entire bandwidth. However, with new radio systems, there is a wish to reduce the bandwidth of the PDCCH space. One bandwidth reduction approach involves allocating a limited sub-band of the overall downlink bandwidth for sending downlink control signaling (in one or a few OFDM symbols).
This small allocation would represent a “common” PDCCH search space to be monitored by all UEs supported by the base station. There may also be a need to configure UE-specific search spaces within the bandwidth allocations made for respective ones of the UEs. Such search spaces may or may not overlap with the common search space, and it will be appreciated that UE-specific search spaces can be configured for each UE by assigning specific RBs within the UE's allocated bandwidth.
When sending a UE-specific message to a given UE, the base station could express resource pointers or other resource identifiers using the resource numbering scheme of the UE. However, consider a PDCCH or other control message that includes a resource pointer or other resource identifier and is intended for more than one UE, e.g., potentially many UEs. The multiple UEs do not necessarily have the same configured bandwidths or the same starting or reference locations for their configured bandwidths within the overall downlink bandwidth. Hence, there is no numbering scheme commonly applicable to the base station and the multiple UEs. Such control messages include, for example, random access response messages, system information related messages, paging messages, broadcast service related messages (like MBMS) etc.
These control messages may contain a reference to a data region where more control content can be found, a pointer to the RBs where, for example, the system info can be found. It is appreciated herein that such a pointer or resource identifier expressed using the resource numbering scheme of the base station will be interpreted differently by UEs having different configured bandwidths or bandwidth positions within the overall downlink bandwidth.
To better appreciate the preceding problem, consider FIG. 1, where the overall downlink bandwidth of interest includes RBs numbered from 0 to 26 by the base station. (N−1)=26. A first UE, denoted as UE 1, operates in an allocated subset of the overall downlink bandwidth and numbers RBs within its allocated bandwidth using a numbering scheme going from 0 to (M1−1)=9. However, “0” within the numbering scheme used by the UE 1 corresponds to “10” within the numbering scheme used by the base station. Similarly, a second UE, denoted as UE 2, operates in another allocated subset of the overall downlink bandwidth and numbers RBs within its allocated bandwidth using a numbering scheme going from 0 to (M2−1)=14. However, “0” within the numbering scheme used by the UE 2 corresponds to “3” within the numbering scheme used by the base station. Note that M1 and M2 are less than or equal to N.
Now consider FIG. 2, which shows a common PDCCH message in RB 10. Of course, it should be appreciated that a PDCCH might in practice span several RBs and the format of the PDCCH message in this example context is not important. What is important is that the PDCCH is intended for more than one UE and includes a resource identifier pointing to a data region (i.e., particular downlink resources) that the UEs should access for further content.
Assume that the data region is located in RBs 12-14 according to the BS numbering. Those same RBs are, however, numbered as RBs 2-4 according to the UE 1 numbering, and are numbered as RBs 9-11 according to the UE 2 numbering. A tempting solution to these numbering differences is to force all UEs to use the same numbering scheme as used by the base station. As recognized herein, however, such an approach has a multiplicity of disadvantages. For example, identifying resources within a smaller number space requires fewer bits than are required for identifying the same resources within a larger number space. Hence, forcing each UE to operate with the larger reference numbering space of the base station forfeits the opportunity to use more efficient resource identifiers for identifying UE-specific resources within the allocated bandwidth associated with a given UE.